Nonwoven products comprise loosely assembled webs or masses of fibers bound together with an adhesive binder. Adequately bonded nonwoven fabrics have advantages over woven fabrics for a large variety of uses. It is known to form bonded nonwoven fabrics by impregnating, printing or otherwise depositing an adhesive bonding composition on a base web of fibers. These fibers may be of cellulosic or polymer maerials such as wood pulp, polyester, polyamides, polyacrylates and the like. The base web of nonwoven fibers to which the binder is applied can be produced by carding, garnetting, air-laying, wet-laying, paper making procedures, or other known operations.
The polymeric binder must imbue the bonded nonwoven product with acceptable dry and wet tensile strengths and solvent resistance for the intended application.
One of the more successful copolymer binder compositions for nonwoven products comprises a vinyl acetate/ethylene/N-methylolacrylamide copolymer. (See U.S. Pat. No. 3,380,851). However, such N-methylolacrylamide (NMA) containing copolymers liberate formaldehyde during cure and subsequent use of the nonwoven.
The nonwovens industry seeks binders yielding ever increasing improvements in water and solvent resistance. In many instances, the nonwoven manufacturer is also demanding that these binders be free of formaldehyde. There are few products that meet both of these requirements.
To improve the water and solvent resistance, i.e. chemical resistance, of a binder, the chemist normally resorts to increasing crosslink density. Unfortunately, the crosslinking monomers most commonly employed contain formaldehyde. In general, the formaldehyde-free crosslinking systems do not offer the high degree of chemical resistance that those containing formaldehyde do.
U.S. Pat. No. 4,505,775 discloses a fibrous, cationic cellulose pulp product and the method of preparing it. A cationic cellulose is made by reaction, under mildly alkaline aqueous conditions, of cellulose fibers with one of a group of condensates based on the reaction product of epichlorohydrin and dimethylamine.